yeah, for a 10 tall, I'd go with just 2 dp's. I've never had a problem with mine and the filter. I used to leave the intake uncovered, but got paranoid and started covering it with a filter media bag. Your idea of a sponge would work really well, soft padding, but might slow down circulaton?
You might also want to put a sponge over the outflow, too, as the current knocked my little guys around. Or try this
http://www.petfish.net/kb/entry/13/347/
I haven't tried the bottle thing yet, but I've heard it works perfectly. Also, if you use sponges, make sure they're designed for aquariums, and not kitchen sponges. Dish sponges often contain antibacterial or antimildew chemicals, that are NOT stated on the package.
Like I said, though, I've never had my dp's have problems around the filter intake, only the outflow. Mine were luckily not in too bad a shape when I got them, so were strong and healthy enough to stay away from it. That outflow, though, they really had to fight.